1. Field of the Invention
The invention relates to a controller for a vehicle power transmission apparatus, and in particular, to improvement of fuel economy during neutral control.
2. Description of the Related Art
For hydraulic pressure supplied to a hydraulic pressure control circuit of a vehicle power transmission apparatus, typically, working fluid that is discharged from a mechanical oil pump that is driven by an engine is supplied as the source pressure. In conventional vehicles, fixed discharge pumps, of which the discharge capacity is invariable, and gear pumps are often used. As described in Japanese Patent Application Publication No. 61-215853 (JP-A-61-215853), for example, an apparatus is already available that includes a first and second pump, and in which the destination of each of these pumps is appropriately changed via an electromagnetic valve depending on the state of the vehicle, whereby the discharge capacity of the entire oil pump is changed.
In recent years, a vehicle power transmission apparatus is realized that is capable of performing neutral control that suppresses the idling load of the engine by bringing a power transmission path into a power transmission suppression state by bringing an engagement device, interposed between an engine and driving wheels in a power transmission path, into a slip state or a release state when predetermined neutral control conditions, such as that the foot brake is in an on state and the vehicle speed is zero while a travel position is selected, are satisfied. A controller for an automatic transmission described in Japanese Patent Application Publication No. 2008-275000 (JP-A-2008-275000) is an example of such an apparatus.
In such a vehicle power transmission apparatus, the load applied to the engine is reduced to improve fuel economy by performing the neutral control. However, the technology for further improving fuel economy is considered necessary from the demand raised by the growing environmental awareness.